The need for using appropriate sensors to carry out industrial oil monitoring has been acknowledge as a critical area by operating engineers, machinery manufacturers and even standard regulation organizations, especially during the last years, wherein the reliability, efficiency and safety on processes and/or products plays a very important role.
Industrial machinery, either energy generating motors or compressors, multipliers, etc. undergoes a lot of stops and failures due to degradation of lubricant and hydraulic oils. This issue causes risky situations when these machines are used as a component of more complex systems, so that the consequence of a stop in these cases is even worst, both from a point of view of cost and machine safety.
The reduction in useful lifetime of the equipment frequently causes unnecessary maintenance costs and current “off-line” measurement methodologies do not provide an early enough detection of the degradation process. Besides, in many environments (transportation, industrial, energy . . . ) this control methodology implies a significant logistic and economic burden for a very small environment. In order to face this issue, a new generation of sensors, capable of carrying out the analysis of the machine in real time, is being developed.
Taking all of the above into account, the use of intelligent sensors will allow in the medium term the optimization of useful lifetime, reducing costs and issues in the machinery. Critical machinery can benefit from an increase in reliability and the operating staff can take advantage of a load reduction in inadequate maintenance work.
The oil degradation process follows several well-known steps: first it undergoes a loss of additives content to later generate acid compounds. The percentage of acid constituents (as additives in the case of new lubricants and as oxidation compounds in the case of operating lubricants) is determined through analytic techniques. There are on-line measuring equipment as the one described in patent JP 2000146696 that use absorbency in the visible range of the electromagnetic spectrum to correlate it with the AN parameter. These methods have the limitation of only contemplating the oxidative degradation of oil, even though AN is one of the most indicative parameters of the lubricant oil state. Besides, this equipment cannot be used in motors due to the carbon generated during the combustion process. Carbon darkens oil, so that the change in color is not due to a change in the state of degradation of oil.
U.S. Pat. No. 7,612,874 introduces a method and device for monitoring oil deterioration in real time. This patent is based in calculating the deterioration by the chromatic ratio Cr=Ur/Ug (absorbency in red and green), to determine the thermic and oxidative deterioration of oil. The method, however, does not allow knowing the remaining life of oil.
U.S. Pat. No. 6,061,139 introduces a method and device for monitoring the thermic degradation of lubricants. This method uses the 850 nm band of light spectrum to determine the state of the oil. The use of a single band causes not having a high sensitivity and the result being affected by other factors.
Patent RU2329502 also uses measurements of the visible light spectrum transmittance with the 3 spectral ranges (red, green and blue) to result in the content of “total impurities”, particles that are generated during oil degradation.